The present invention relates to a semiconductor laser, a method of producing the semiconductor laser and an evanescent optical head using the semiconductor laser, particularly to a semiconductor laser that can be easily formed with a small opening for emitting evanescent light, a method of producing the semiconductor laser and an evanescent optical head using the semiconductor laser.
Recent advances in telecommunications technology are increasing demand for higher capacity data recording media such as optical disks. One key to achieving high-capacity optical disks and other data recording media is to increase recording density by reducing the spot diameter of the laser used for reading and writing data from/to the medium. Many attempts have been made to reduce spot diameter by shortening the wavelength or increasing the numerical aperture (NA) of the laser beam source.
Separately from these attempts focused on shortening the wavelength or increasing the numerical aperture (NA) of the laser beam source, another approach has been pursued based on use of evanescent light for reading and writing data from/to optical disks and other such media, as taught, for example, by Japanese Patent Application Laid-Open No. 9-145603. Evanescent light, also called xe2x80x9cnear-field light,xe2x80x9d is produced when light passes through a small opening of a diameter considerably smaller than the wavelength of the light source. This is known as one way of obtaining evanescent light. When evanescent light is used for read/write of optical disks and other media, the laser spot diameter can be reduced substantially independently of the laser beam source wavelength. This means that use of evanescent light for read/write of optical disks and the like has the potential to enhance the recording density of such data recording media and thus increase their recording capacity.
When a semiconductor laser is used to produce evanescent light, substantially the total area of the light-emitting end face of the semiconductor laser, including the light-emitting region from which the laser beam actually exits, is first formed with a light-shielding film and then part of the portion of the light-shielding shield film over the light-emitting region is removed to form a small opening. As this enables emission of evanescent light from the small opening, use of the semiconductor laser in a head for read/write of an optical disk or the like makes it possible to increase the recording capacity of the recording medium.
When evanescent light is to be obtained using a semiconductor laser, therefore, the light-shielding film formed on the light-emitting end face of the semiconductor laser has to be removed at one part of the portion corresponding to the light-emitting region. However, the location of the portion of the light-shielding film corresponding to the light-emitting region is extremely difficult to determine. This is because once the light-shielding film has been formed on the light-emitting end face of the semiconductor laser, the layer structure of the semiconductor laser can no longer be visually ascertained and there is no way of visually determining what portion of the light-shielding film formed on the light-emitting end face of the semiconductor laser corresponds to the light-emitting region.
Conventionally, therefore, an operation has been required for determining the point at which the small opening should be formed by in advance measuring the distance of the light-emitting region from external features of the semiconductor laser such as projections occurring on the upper and lower faces lying perpendicular to the light-emitting end face. Since the size of the light-emitting region is much smaller than the outer dimensions of the semiconductor laser, however, it is hard to form the small opening at exactly the right location by this kind of operation. Ascertaining the location at which the small opening should be formed is particularly difficult when the semiconductor laser has no distinctive external features, such as when the upper, lower and lateral surfaces are all flat.
It is therefore an object of the present invention to provide a semiconductor laser that can be easily formed with a small opening for emitting evanescent light and a method of producing the semiconductor laser.
Another object of the present invention is to provide an evanescent optical head equipped with a semiconductor laser that can be easily formed with a small opening for emitting evanescent light.
In one aspect of the present invention, the above and other objects are accomplished by a semiconductor laser having a laser beam-emitting end facet including a laser beam-emitting region, the semiconductor laser comprising a three-dimensional feature portion indicating the location of the light-emitting region formed on the laser beam-emitting facet at a region different from the light-emitting region.
In this aspect of the present invention, since the three-dimensional feature portion indicating the location of the light-emitting region is formed on the laser beam-emitting facet at a region different from the light-emitting region, the location of the light emitting region can be ascertained by referring to the three-dimensional feature portion.
In a preferred embodiment of the present invention, the three-dimensional feature portion is at least one of a concavity and a convexity formed on the laser beam-emitting facet at a region different from the light-emitting region.
In another preferred embodiment of the present invention, the semiconductor laser further comprises a light-shielding film covering at least the light-emitting region, the light-shielding film being formed with a small opening at part of the portion over the light-emitting region.
In this preferred embodiment, the location of the light-emitting region can be ascertained by referring to the three-dimensional feature portion even after the light-emitting region has been covered by the light-shielding film. The location at which the small opening should be formed can therefore be determined accurately and simply.
In another preferred embodiment of the present invention, the light-shielding film further covers the three-dimensional feature portion.
In this preferred embodiment, the portion of the light-shielding film covering the three-dimensional feature portion reflects the three-dimensional feature. The location at which the small opening should be formed can therefore be determined accurately and simply by referring to this portion.
In another preferred embodiment of the present invention, the semiconductor laser further comprises a dielectric film provided between the laser beam-emitting facet and the light-shielding film, part of the dielectric film being exposed at the small opening.
In another aspect of the present invention, the above and other objects are accomplished by a method of producing a semiconductor laser having a laser beam-emitting facet including a laser beam-emitting region comprising a step of forming a three-dimensional feature portion at a location on the laser beam-emitting facet to have a prescribed positional relationship with the light-emitting region.
In this aspect of the present invention, since the three-dimensional feature portion is formed at a location on the laser beam-emitting facet to have a prescribed positional relationship with the light-emitting region, the location of the light-emitting region can be ascertained by referring to the three-dimensional feature portion.
In another preferred embodiment of the present invention, the method further comprises a step of forming a light-shielding film covering at least the light-emitting region and a step of forming the light-shielding film with a small opening at a location to have a prescribed positional relationship with the three-dimensional feature portion.
In this preferred embodiment, the location at which the small opening should be formed can be accurately and simply determined by referring to the three-dimensional feature portion even after the light-emitting region has been covered by the light-shielding film.
In another preferred embodiment of the present invention, the step of forming the three-dimensional feature portion and the step of forming the small opening both utilize focused ion beam (FIB) processing.
In this preferred embodiment, no special equipment is required for forming the three-dimensional feature portion because the two steps utilize FIB processing. Increase in semiconductor laser production cost can therefore be minimized.
In another preferred embodiment of the present invention, the method further comprises a step of irradiating at least the light-emitting region of the laser beam-emitting facet with an FIB before the step of forming the three-dimensional feature portion.
In this preferred embodiment, since the light-emitting region is irradiated with FIB before the step for forming the three-dimensional feature portion, the layer structure of the laser beam-emitting facet can be visually ascertained and, in addition, oxide film formed on the light-emitting region and impurities adhering to the light-emitting region can be removed.
In another aspect of the present invention, the above and other objects are accomplished by an evanescent optical head for reading/writing of data from/to a recording medium using evanescent light, the evanescent optical head being equipped with a semiconductor laser for emitting the evanescent light that comprises a laser beam-emitting facet including a light-emitting region, a three-dimensional feature portion formed on the laser beam-emitting facet, a light-shielding film covering at least the light-emitting region, and a small opening for emitting the evanescent light formed in the light-shielding film at a location to have a prescribed positional relationship with the three-dimensional feature portion.